Generally, the widely-used peripheral input device of a computer includes for example a mouse device, a keyboard device, a trackball device, or the like. Via the keyboard device, the user may directly input characters and symbols into the computer. As a consequence, most users and most manufacturers of the input devices pay much attention to the keyboard devices.
Hereinafter, the configurations and the functions of a conventional keyboard device will be illustrated with reference to FIG. 1. FIG. 1 is a schematic top view illustrating the outward appearance of a conventional keyboard device. As shown in FIG. 1, plural keys 10 are installed on a surface of the conventional keyboard device 1. These keys 10 are classified into some types, e.g. ordinary keys, numeric keys and function keys. When one or more keys 10 are depressed by the user's fingers, a corresponding electronic signal is issued to the computer, and thus the computer executes a function corresponding to the depressed key or keys. For example, when an ordinary key is depressed, a corresponding English letter or symbol is inputted into the computer. When a numeric key is depressed, a corresponding number is inputted into the computer. In addition, the function keys (F1˜F12) can be programmed to cause corresponding application programs to provide certain functions.
Hereinafter, the components of a key structure of the conventional keyboard device will be illustrated with reference to FIG. 2. FIG. 2 is a schematic exploded view illustrating a key structure of a conventional keyboard device. As shown in FIG. 2, the key structure 2 comprises a keycap 21, a scissors-type connecting member 22, an elastic element 23, a membrane switch circuit 24, and a base plate 25. The keycap 21 may be touched and depressed by the user. In addition, the keycap 21 is connected with the scissors-type connecting member 22. The scissors-type connecting member 22 is arranged between the keycap 21 and the base plate 25. In addition, the scissors-type connecting member 22 is connected with the keycap 21 and the base plate 25. The scissors-type connecting member 22 comprises an inner frame 221 and an outer frame 222. The inner frame 221 has a rotating shaft 2211. The outer frame 222 has two openings 2221 corresponding to the rotating shaft 2211. After the rotating shaft 2211 is penetrated through the openings 2221, the inner frame 221 and the outer frame 222 are connected with each other, and the inner frame 221 is swingable relative to the outer frame 222. The membrane switch circuit 24 is disposed on the base plate 25. The elastic element 23 is arranged between the keycap 21 and the membrane switch circuit 24. When the keycap 21 is depressed, the elastic element 23 is deformed downwardly to trigger the membrane switch circuit 24, so that the membrane switch circuit 24 generates a corresponding electronic signal.
In a case that the key structure 2 is not depressed, the keycap 21 of the key structure 2 is located at a first height (not shown). Whereas, when the key structure 2 is depressed, a downward pressing force is exerted on the keycap 21, and the elastic element 23 is compressed in response to the pressing force. Moreover, as the keycap 21 is depressed, the inner frame 221 and the outer frame 222 of the scissors-type connecting member 22 are correspondingly swung with the keycap 21. Consequently, the inner frame 221 and the outer frame 222 are parallel with each other. At the same time, the membrane switch circuit 24 on the base plate 25 is pressed and triggered by the elastic element 23. Consequently, the membrane switch circuit 24 generates a corresponding electronic signal. Meanwhile, the keycap 21 of the key structure 2 is descended from the first height to a second height (not shown). The difference between the first height and the second height indicates a travelling distance of the key structure 2.
In a case that the pressing force exerted on the keycap 21 is eliminated, the keycap 21 will be moved upwardly in response to a restoring force of the elastic element 23. As the keycap 21 is moved upwardly, the inner frame 221 and the outer frame 222 are towed by the keycap 21 and correspondingly rotated. Consequently, the keycap 21 is returned to its original position where the keycap 21 has not been depressed (i.e. at the first height).
From the above discussions, after the pressing force exerted on the keycap 21 is eliminated, the keycap 21 should be moved upwardly and returned to its original position (i.e. at the first height). For achieving this purpose, the elastic element 23 should provide a sufficient restoring force to push the keycap 21 back to its original position. In addition, the inner frame 221 and the outer frame 222 need to cooperate with each other to precisely control the upward moving action of the keycap 21 in the vertical direction. In other words, the performance of the scissors-type connecting member 22 is a very important factor that influences the quality and the use life of the key structure 2. Moreover, for combining the inner frame 221 with the outer frame 222, the user needs to prop open the outer frame 222 to widen the distance between the two openings 2221, which are respectively located at bilateral sides of the outer frame 222. Consequently, the rotating shaft 2211 can be successfully inserted into the openings 2221 to result in the combination between the inner frame 221 and the outer frame 222. The procedure of propping-open the outer frame 222 increases the assembling time of the key structure 2 and is detrimental to the throughput of the keyboard device. Moreover, since the outer frame 222 has the openings 2221, if the thickness of the key structure 2 is slimed, the whole structure of the outer frame 222 becomes weak and is easily damaged. In other words, the conventional scissors-type connecting member 22 is not suitable for slimness of the key structure 2.